Process for cyclo-dehydrating ketoses

ABSTRACT

The invention concerns a process for dehydrating glucides and applicable to those glucides of which the molecule includes at least one ketose type group, being characterized in that the glucide is made to react without addition of water with a hydrogen halide, whereupon the hydrogen halide is eliminated by evaporation in order to collect the formed disaccharide anhydride. 
     The invention also relates to novel products characterized by essentially consisting of saccharide anhydrides of which the molecule includes two saccharide cycles linked to each other by two acetal bonds included in a dioxane cycle. As a rule at least one of the saccharide cycles is that of fructose (and may be substituted), and this cycle is linked by a spirane bond to the dioxane cycle. 
     Product application as food additives.

The object of the invention is a process for cyclodehydrating ketoses,the obtained products, and their use as food additives.

More particularly, the invention concerns the field of substitutes forfood sugars.

Products substituting for food sugars have already long been sought inorder to avoid the vexatious consequences of excessive consumption ofthese food sugars.

For instance, it has already been suggested to use products which whileevincing a more or less pronounced sweetening effect are alsocharacterized by not being metabolized by the human organism. Theseproducts also are termed "non-caloric food sugars." The sizeablesweetening effect of a dipeptide, namely the methylester of thealpha-aspartyl phenylanilin (or aspartame), described in particular inFrench Pat. No. 1,577,545 has already been long known.

One of the problems related to using aspartame as a sweetener is that inthe light of its high sweetening effect, this compound can only be usedin small amounts. Furthermore, it is present only in the crystallineform. To make it acceptable to the consumer, it must therefore beassociated with a neutral excipient.

The purpose of the invention, therefore, is to propose glucide analoguesof which some are novel products per se and which due to their featuresof being not assimilated by the organism are capable of entering eitheralone or in mixture the composition of a non-caloric food sugar, orwhich can be used as an excipient for a conventional or synthesizedsweetener so as to make possible an association with a sweetening powerwhich is equal or higher, but always non-caloric.

Another purpose of the invention is to propose a process foradvantageously synthesizing these products.

The process for cyclo-dehydrating glucides of which the moleculeincludes at least one ketose-type group is characterized in that withoutadding water, the glucide is made to react with a hydrogen halide actingas the glucide solvent, and in that the hydrogen halide is eliminated ina dry manner.

The hydrogen halides are selected from the hydrogen iodides, bromides,chlorides, or fluorides. Among these, hydrogen chloride and hydrogenfluoride result in substantially higher yields in dehydrated compoundssince the reaction in the presence of hydrogen bromide or iodide resultsin a high proportion of waste residues.

Advantageously hydrogen chloride or fluoride will be used because thesehalides allow making products at excellent yields. Hydrogen fluoride isthe preferred halide because it results in practically quantitativeyields.

The glucides of which the molecule includes at least one ketose-typegroup can be ketotetroses, ketopentoses, or ketohexoses. They may be inmonomeric or polymeric form, the latter expression including the dimers.

Advantageously the glucides with a ketopentose group are selected fromxylulose or one of its polymers.

The glucides with a ketohexose group are the preferred glucides forimplementing the process of the invention. Among these areillustratively fructose, inulin, and sorbose.

The invention further includes the above-cited glucides of which themolecules comprise one of or more substitutents of ether, ester, acetalor other type, and in a position such as not to hamper thecyclo-dehydration reaction.

Of all of these compounds, those glucides are preferred wherein at leastone of the saccharide cycles is fructose is sorbose.

The reaction takes placed without added water. This does not mean ittakes place anhydrously because-a dehydration process beinginvolved-water is automatically being formed as the reaction proceedstoward the dehydrated compounds. Additionally, the initial products maybe partly hydrated.

However, the proportion of water at the end of the reaction may notexceed 10% by weight of the final reaction mixture in order not todecrease the yield in dehydrated compounds.

However, in a preferred variation, the halide is introduced dry.Similarly, the sugar to be reacted is previously dried so it shall nolonger contain any water except the water of crystallization.

The glucide may be made to contact the halide in a variety of ways.Thus, the halide may be circulated in the gaseous state, under pressure,or entrained while diluted in an inert carrier gas such as nitrogen orsulfur dioxide.

When the invention was implemented, the process effectiveness appearedto be directly related to the dissolution of the processed glucide inthe hydrogen halide. Preferably, therefore, the glucide is dissolved inthe halide in the liquid state and advantageously the glucide shall becompletely dissolved in the halide. The reaction temperatureadvantageously is between -20° C. and +25° C. Thereafter the halide iseliminated by any suitable means, for instance by evaporation inparticular.

The reaction may be partial, but nevertheless results in products ofwhich the application is explained below.

Preferably the hydrogen halide is made to react in molar excess withrespect to the number of ketose monosaccharide equivalents.

Advantageously the molar ratio of hydrogen halide to ketosemonosaccharide equivalents is between 5 and 100, and better yet between6 and 50.

The process of the invention results in saccharide dianhydrides whichare easily isolated by crystallization; and, furthermore, they areobtained in the pure state at very high yields. Be it noted too thatregardless of the initial glucide, the reaction appears to favor formingthe ketose dimer in the dianhydrides of the invention.

Another object of the present invention are the products obtained by theabove-described process.

Another object of the invention is the novel products consisting ofsaccharide anhydrides which are characterized in being essentiallyformed by saccharide dianhydrides of which the molecule comprises twosaccharide cycles linked to each other by two acetal bonds included in adioxane cycle.

Preferably at least one of the saccharide cycles is a ketose type cycle,in particular that of fructose, and this cycle is linked to the dioxanecycle by a spirane bond.

It is known that the ketoses are glucides which, contrary to the case ofthe aldoses, include at least one ketone function.

However, it must be borne in mind that the fructose or other ketosecycle may be substituted. In other words, in the above expression, notonly are we including the fructose proper, but also the homologousketoses, the isomers with a configuration like the sorbose, and theketoses of which the molecule comprises one or more substituents of theether, ester, acetal or other type.

Preferably the anhydrides consist in part of D-fructose dianhydrides.

Preferably the anhydrides essentially consist of a mixture ofdianhydrides of di-D-fructopyranose and/or fructofuranose andfructopyranose.

More particularly, the invention includes the following novel products:

di-alpha-d-fructopyranose 1,2':2,1' dianhydride

beta-D-fructofuranose beta-D-fructopyranose 1,2':2,1' dianhydride

beta-D-fructofuranose alpha-D-fructopyranose 2,1':3,2' dianhydride

sorbose dianhydride.

Another object of the invention is the application of theabove-described products possibly obtained by the previously describedprocess as food additives.

Remarkably the products of the invention are both non-toxic andnon-hydrolyzing, whereby they constitute non-assimilated foods. Due totheir structure, moreover, it is clear that even if they were destroyedwithin the organism, their hydrolysis would only result in non-toxicproducts consisting of sugar molecules, in particular fructose. Thepresence of these products in food sugar allows decreasing the caloricpower of sugar and of the foods into which they are incorporated.

The products of the invention can be prepared by dehydrating knownsugars. If, for instance, saccharose is involved, even a partialdehydration results in a less caloric sugar than the initial product.Therefore, another object of the invention is a process for treatingsugars to decrease their caloric power and characterized essentially byproviding at least a partial dehydration of the sugar in conditionsleading to the formation of acetal bonds between the saccharide cycles.

Furthermore, some of these products provide a sweet taste while othersare wholly tasteless (neutral taste). They are crystallized andwater-soluble. Therefore, they can be advantageously combined with awell-known sweetener such as aspartame, acesulfam, saccharin, or thelike.

Accordingly, another object of the invention is a food productcontaining 1% to 10% by weight of aspartame or the like, and 90% to 99%of one of the compounds of the invention.

The invention is illustrated below by particular implementing examples.

EXAMPLE I

5 g of inulin from Sigma dahlia tubers, cooled to 0° C., receive 10 mlof hydrogen fluoride which also are cooled. The solution is allowed tostand at room temperature (20° C.) for about 45 minutes, whereupon thehydrogen fluoride is evaporated by pressure reduction or by beingentrained in a gas flow. The residue is then reprocessed with ether.

4.8 g of a product consisting of D-fructose anhydrides and identifiedchromatographically in the gaseous phase as methylated products arerecovered. The product appears being formed by a mixture including inpercent by weight of the total weight of the following:

12% of (1):di-alpha-D-fructopyranose 1,2':2,1' dianhydride

Melting point: 293°-295° C.

Rotation [α]_(D) :-46°.

14% of (2):di-beta-D-fructopyranose 1,2':2,1' dianhydride

Melting point: 279° C.

Rotation [α]_(D) :-300°.

45% of (3):alpha-D-fructofuranose alpha-D-fructopyranose 1,2':2,1'dianhydride

Melting point: 258° C.

Rotation [α]_(D) :-39°.

4% of (4):beta-D-fructofuranose beta-D-fructopyranose 1,2':2,1'dianhydride

Melting point: 240° C.

Rotation [α]_(D) :-182°.

18% of (5) : beta-D-fructofuranose alpha-D-fructopyranose 2,1':3,2'dianhydride

Melting point: 206° C.

Rotation [α]_(D) :-58.5°.

EXAMPLE II

20 g of D-fructose are treated with 20 ml of hydrogen fluoride (HF) at-10° C. for three minutes, then the hydrogen fluoride is evaporatedusing air at reduced pressure. Cooled diethylether is added to theresidue. The precipitate is decanted and reprocessed several times withdiethylether, then decanted and filtered.

18.4 g of a product consisting of a mixture of D-fructose dianhydrides,chromatographically identified in the gaseous phase and denoted as inExample I are recovered. In percent of weight with respect to the totalweight, the mixture includes:

14% of (1)

20% of (2)

58% of (3)

7% of (5)

By varying the conditions, that is the amount of HF (1 ml per 1 g as aminimum to 10 ml per 1 g), the temperature (-10° C. to +20° C.) and thetime (from 2 minutes to 5 hours), sugars are obtained which essentiallyconsist of the same five compounds already identified in Example I,though in different proportions, within the distributions below:

from 10% to 20% for (1)

from 10% to 20% for (2)

from 30% to 60% for (3)

from 4% to 8% for (4)

from 10% to 30% for (5)

EXAMPLE III

18.4 g of the mixture obtained in Example II (first section) areprocessed with 20 ml of methanol and made to crystallize. The compounds(1) and (2) are directly recovered (4 g).

The dried mother liquors solely consist of the derivatives (3), (4), and(5). The derivative (3) is the main derivative (40%) of the mixture, andis crystallized by adding seed-forming crystals to the mother liquorsreprocessed in ethanol. The product purity is about 98%.

Proceeding in the same manner but using a mixture obtained per ExampleII, under different conditions, this compound (3) is obtained with ayield of 60%.

EXAMPLE IV

Proceeding in cold conditions as in Example I, 10 g of L-sorbose aretreated with 10 ml of HF for one minute at -10° C. The product isprecipitated with diethylether. The amount recovered is 9.2 g. This is amixture of several compounds identified as being L-sorbose dianhydrides.The following compounds are sequentially identified chromatographicallyin the gaseous phase and by carbon nuclear magnetic resonance:

di-alpha-L-sorbopyranose 1,2':2,1' dianhydride

di-beta-L-sorbopyranose 1,2':2,1' dianhydride

alpha-L-sorbofuranose alpha-L-sorbopyranose 1,2':2,1' dianhydride

alpha-L-sorbofuranose beta-L-sorbopyranose 1,2':2,1' dianhydride

alpha-L-sorbofuranose beta-L-sorbopyranose 1,2':3,1' dianhydride

The products can be isolated in the same manner as for D-fructose(Example II) by adding methanol, then ethanol.

EXAMPLE V

5 g of saccharose are mixed with 10 ml of hydrogen fluoride at 0° C. Themixture is allowed to react for 2.5 minutes, then the product isprecipitated with ether. 4.8 g are recovered.

The mixture so obtained contains glucosyl fluoride (analyzed using .sup.13C nuclear magnetic resonance). Study of the methylated products showsthe presence of D-fructose dianhydrides; the five compounds defined inExample I are present.

In quantitative terms, the mixture contains 18% of D-fructose in theform of dianhydrides.

Due to treatment with hydrogen fluoride, the initial saccharose,therefore, has become enzymatically non-hydrolyzing and its caloricpower is decreased.

EXAMPLE VI

The products from the Examples I through IV are checked for theproperties allowing to use them as saccharose substitutes in foodstuffs.

These products are non-toxic. They are all water-soluble, and the syrupsprepared vary in viscosity as a function of concentration the way commonsugar does.

Illustratively the last mixture of D-fructose anhydrides prepared perExample II is not hydrolyzed by 0.01N HCl at 37° C. for 0.5 hour. As arule, the hydrolysis rate at 20° C. and in the presence of 1N sulfuricacid of the various compounds is about 1,000 times less than that ofsaccharose.

Furthermore, when a partly treated mixture containing dianhydrides issubjected to fermentation by brewer's yeast, the untransformed sugarswill be sensitive to the yeast and can be eliminated, whereas thedianhydrides of the invention are left unaffected.

EXAMPLE VIII

5 g of xylulose syrup are treated with 10 ml of liquid hydrogen fluoridefor 2 minutes at -10° C. Ethylether is then added to this solution.Following decanting, 4.5 g of the products below are collected:

di-alpha-D-xylulofuranoside 1,2'-2,1' dianhydride

di-beta-D-xylulofuranoside 1,2'-2,1' dianhydride

alpha-D-xylulofuranoside beta-D-xylulofuranoside 1,2'-2,1' dianhydride

alpha-D-xylulofuranoside beta-D-xylulofuranoside 1,2'-3,1' dianhydride.

We claim:
 1. A process for cyclo-dehydrating glucides of which themolecule includes at least one ketose type group, characterized in thatthis glucide is made to react without added water with hydrogen fluorideused as a solvent for the glucide, whereupon the hydrogen fluoride iseliminated in a dry manner.
 2. Process per claim 1, characterized inthat the initial glucide is selected from fructose, saccharose, inulin,and sorbose.
 3. Process per claim 1, characterized in that the molarratio of hydrogen fluoride to said ketose is between 5 and
 100. 4.Process per claim 1, characterized by being carried out in suchconditions that the amount of water present in the reaction medium priorto eliminating the hydrogen fluoride is less than 10% by weight. 5.Process per claim 1, characterized in that the reaction is carried outwith the hydrogen fluoride in the liquid state.
 6. Process per claim 5,characterized in that the temperature of the reaction medium is between-20° C. and +25° C.
 7. Process per claim 5, characterized by thehydrogen fluoride being eliminated by evaporation following thereaction.
 8. Process per claim 1, characterized in that the molar ratioof hydrogen fluoride to said ketose is between 6 and
 50. 9. Glucideanhydrides obtained by the process of claim 1.